A balun, sometime referred to as a balun transformer, is a two port device or circuit that transforms a signal from a balanced transmission line into a signal for an unbalanced transmission line and vice versa. The balun has an unbalanced port, referenced to ground, and a balanced port with two terminals—each referenced to the other. This is generally described in U.S. Pat. No. 8,638,181 to Gerst, et al., which is hereby incorporated by reference for all purposes. Balun transformers are used to transform balanced and unbalanced signals in, for example, antenna feed circuitry and push-pull amplifiers.
The “Guanella balun” is a well-known circuit configuration that is characterized by its impedance ratios. More specifically, an x:y Guanella balun has an unbalanced port impedance that is x/y times its balanced port impedance where Guanella baluns with ratios of 1:1, 1:4 and 4:1 are common. Known Guanella baluns use magnetic material in order to increase the impedance seen by common mode currents as a higher common mode impedance improves the balun performance.
As discussed in U.S. Pat. No. 9,276,056 to Akhtar, et al., which is hereby incorporated by reference for all purposes, radio frequency (RF) circuitry uses differential signaling to eliminate common mode noise and increase dynamic range. The signals received by an antenna, or transmitted by an antenna, however, are single-ended and a balun is implemented to convert from single-ended to differential or from differential to single-ended. In addition to providing signal conversion, baluns also provide impedance transformation between preceding and following stages for maximizing power and signal transfer.
Akhtar, et al., also disclose a balun having a differential primary (or secondary) inductor winding and a single-ended secondary (or primary) inductor formed in a stacked configuration. The balun is formed using layers of metal available in a CMOS fabrications process.
What is needed, however, is an improved balun device.